The invention relates to novel fluorocyclohexene derivatives of the formula I
R1xe2x80x94(A1xe2x80x94Z1)nxe2x80x94Axe2x80x94(Z2xe2x80x94A2)mxe2x80x94Z3xe2x80x94Bxe2x80x94(Z4xe2x80x94A3)pxe2x80x94R2xe2x80x83xe2x80x83I
in which
R1 and R2, independently of one another, are H or an alkyl radical having 1-12 carbon atoms which is unsubstituted or at least monosubstituted by halogen or CN and in which, in addition, one or more CH2 groups may each, independently of one another, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, 
xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 in such a way that heteroatoms are not connected directly, 
A1, A2 and A3, independently of one another, including if they occur more than once, are
a) a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
d) 1,4-cyclohexenylene, 
xe2x80x83where the radical b) may be monosubstituted or polysubstituted by CN, Cl or F,
B, is a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94, 
xe2x80x83X1 and X2, independently of one another, are H, F, Cl, CN, CF3 or CHF2,
Z1, Z2,
Z3 and 4 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1xe2x80x94Cxe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94OCF2, xe2x80x94CF2Oxe2x80x94, xe2x80x94CHxe2x95x90CFxe2x80x94, xe2x80x94CFxe2x95x90CHxe2x80x94 or a single bond,
and
n, m and p, independently of one another, are 0, 1, 2 or 3,
where
m+n+p is 0, 1, 2 or 3.
The invention also relates to the use of the compounds of the formula I as components of liquid-crystalline media, and to liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.
The compounds of the formula I frequently have a highly negative value of the dielectric anisotropy and can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases (DAP) or electrically controlled birefringence (ECB) or the effect of dynamic scattering.
DE 4227772 A1 discloses compounds containing fluorocyclohexene rings. However, this document only describes compounds which contain a terminal fluorocyclohexene ring in combination with a perfluoroalkyl radical bonded thereto.
The compounds according to the invention are also covered by a very broad generic claim in DE 4427266 A1, which is directed towards compounds of positive dielectric anisotropy which contain a terminal, optionally fluorinated phenyl radical in combination with a fluorocyclohexene ring. The compounds of the present application are, however, not explicitly mentioned therein.
The substances employed hitherto for this purpose all have certain disadvantages, for example inadequate stability to the action of heat, light or electric fields, or unfavourable elastic and/or dielectric properties.
The invention had the object of finding novel, stable, liquid-crystalline or mesogenic compounds having a broad nematic phase range and negative dielectric anisotropy which are suitable as components of liquid-crystalline media, in particular for TFT and STN displays.
It has now been found that the compounds of the formula I are eminently suitable as components of liquid-crystalline media. They can be used to obtain stable liquid-crystalline media, in particular suitable for TFT or STN displays. The novel compounds are distinguished, in particular, by high thermal stability, which is advantageous for a high xe2x80x9cholding ratioxe2x80x9d, and exhibit favourable clearing point values.
The provision of compounds of the formula I very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
The compounds of the formula I have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add compounds of the formula I to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity. The addition of compounds of the formula I to liquid-crystalline dielectrics allows the xcex94xcex5 values of such media to be significantly reduced.
The meaning of the formula I covers all isotopes of the chemical elements bound in the compounds of the formula I. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for producing chiral mesophases.
In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. They are stable chemically, thermally and to light.
The invention thus relates to the compounds of the formula I and to the use of these compounds as components of liquid-crystalline media. The invention furthermore relates to liquid-crystalline media comprising at least one compound of the formula I, and to liquid-crystal display elements, in particular electro-optical display elements, which contain media of this type.
Above and below, n, m, p, R1, R2, A, B, Z1, Z2, Z3, Z4, A1 and A2 and A3 are as defined above, unless expressly stated otherwise. If the radical A1 occurs more than once, it can have the same or different meanings. The same applies to all other groups which occur more than once.
For reasons of simplicity, Cyc below denotes a cyclohexane-1,4-diyl radical, Dio denotes a 1,3-dioxane-2,5-diyl radical, Phe denotes a 1,4-phenylene radical, Dit denotes a 1,3-dithiane-2,5-diyl radical, and Bi denotes a bicyclo[2.2.2]octylene radical, where Cyc and Phe may be unsubstituted or mono- or polysubstituted by halogen or CN, preferably F or CN.
PheXX below denotes 
wherein X1 and X2, independently of one another, are H, F, Cl, CN, CF3 or CHF2, preferably at least one of X1 and X2 is F and the other one H or F.
CheF below denotes 
The formula I covers the preferred compounds of the sub-formulae Ia1 to Ia2:
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ia1
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ia2
The formula I covers the preferred compounds of the sub-formulae Ib1 to Ib27, which, in addition to the CheF and PheXX groups, contain a further six-membered ring:
R1xe2x80x94CheFxe2x80x94Cycxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib1
R1xe2x80x94Cycxe2x80x94CH2CH2xe2x80x94CheFxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib2
R1xe2x80x94Cycxe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib3
R1xe2x80x94Dioxe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib4
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib5
R1xe2x80x94Chefxe2x80x94Phexe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib6
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94Phexe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib7
R1xe2x80x94Dioxe2x80x94CH2CH2xe2x80x94Dioxe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib8
R1xe2x80x94Phexe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib9
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94Phexe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib10
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib11
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib12
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94CH2CH2xe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib13
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94CHxe2x95x90CHxe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib14
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94Cxe2x89xa1Cxe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib15
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94CH2CH2xe2x80x94Phexe2x80x94R2xe2x80x83xe2x80x83Ib16
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94Cycxe2x80x94R2xe2x80x83xe2x80x83Ib17
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94Cycxe2x80x94R2xe2x80x83xe2x80x83Ib18
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R2xe2x80x83xe2x80x83Ib19
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R2xe2x80x83xe2x80x83Ib20
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94Dioxe2x80x94R2xe2x80x83xe2x80x83Ib21
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94Dioxe2x80x94R2xe2x80x83xe2x80x83Ib22
R1xe2x80x94Chefxe2x80x94PheXXxe2x80x94CheFxe2x80x94R2xe2x80x83xe2x80x83Ib23
xe2x80x83R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94CheFxe2x80x94R2xe2x80x83xe2x80x83Ib24
R1xe2x80x94CheFxe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib25
R1xe2x80x94CheFxe2x80x94CH2CH2xe2x80x94CheFxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib26
R1xe2x80x94CheFxe2x80x94CheFxe2x80x94CH2CH2xe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ib27
furthermore the likewise preferred compounds of the sub-formulae Ic1 to Ic5, which, in addition to the CheF and PheXX groups, contain two six-membered rings:
R1xe2x80x94Cycxe2x80x94Cycxe2x80x94Chefxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ic1
R1xe2x80x94Cycxe2x80x94Chefxe2x80x94Phexe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ic2
R1xe2x80x94Dioxe2x80x94Chefxe2x80x94Phexe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ic3
R1xe2x80x94Cycxe2x80x94CheFxe2x80x94Cycxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ic4
R1xe2x80x94CheFxe2x80x94Cycxe2x80x94Cycxe2x80x94PheXXxe2x80x94R2xe2x80x83xe2x80x83Ic5
in which R1, Cyc, Dio, CheF, PheXX and R2 are as defined above.
PheXX in the above-mentioned formulae preferably has the following meaning: 
R1 and R2 are preferably, independently of one another, straight-chain alkyl or alkoxy having 1 to 10 carbon atoms or alkenyl or alkenyloxy having 2 to 10 carbon atoms, in particular alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl having 2 to 7 carbon atoms.
In particularly preferred compounds of the formula I, a radical R1 or R2 which is not bonded to an aromatic ring, but instead to a saturated ring, such as Cyc or Dio, is preferably alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl having 2 to 7 carbon atoms, while a radical R1 or R2 which is bonded to an aromatic ring is preferably alkyl or alkoxy having 1 to 7 carbon atoms, in particular alkoxy.
R2 is particularly preferably alkoxy having 1 to 7 carbon atoms.
Particular preference is furthermore given to compounds of the formula I in which A1, A2 and/or A3 have one of the following meanings: 
B preferably has the following meaning: 
m and n are preferably 0 or 1. m+n is preferably 0 or 1. p is preferably 0.
Z1, Z2, Z3 and Z4 are preferably, independently of one another, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or a single bond, particularly preferably a single bond or xe2x80x94CH2xe2x80x94CH2xe2x80x94.
X1 and X2 are preferably simultaneously F or CN, in particular F.
Particular preference is given to compounds of the formulae IA: 
Compounds of the formula I which contain not more than one dioxane ring likewise represent a preferred embodiment of the invention.
Particular preference is furthermore given to the compounds of the formulae I1 to I16 from the following group: 
in which R1, R2, X1, X2, Z1, Z2 and Z3 are as defined above, and L1, L2 and L3, independently of one another, are H or F.
Some very particularly preferred smaller groups of compounds of the formula I are those of the sub-formulae I17 to I23: 
The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart) to be precise under reaction conditions which are known and suitable for said reactions.
Use can be made here of variants which are known per se, but are not mentioned here in greater detail.
If desired, the starting materials can also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the formula I.
The compounds of the formula I are preferably obtainable by dehydrofluorination of compounds of the formula II by means of bases:
R1xe2x80x94(A4xe2x80x94Z5)nxe2x80x94A*xe2x80x94(Z6xe2x80x94A5)mxe2x80x94Z7xe2x80x94B*xe2x80x94(Z8xe2x80x94A6)pxe2x80x94R2xe2x80x83xe2x80x83II
in which 
and
A4, A5 and A6, independently of one another, including if they occur more than once, are
a) a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, deca-hydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
d) 1,4-cyclohexenylene, 
xe2x80x83where the radical b) may be monosubstituted or polysubstituted by CN, Cl or F, and the radical a) may be monosubstituted by Cl or F,
Z5, Z6,
Z7 and Z8 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94CH2CF2xe2x80x94, xe2x80x94CF2CH2xe2x80x94 or a single bond,
B*, independently of one another if it occurs more than once, is a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94and/or xe2x80x94Sxe2x80x94, 
and
R1, R2, X1, X2, n, m and p are as defined above.
Of the compounds of the formula II, particular preference is given to the novel difluorocyclohexanes of the sub-formula III
R3xe2x80x94A*xe2x80x94(Z6xe2x80x94A7)mxe2x80x94Z7xe2x80x94Qrxe2x80x94R7xe2x80x83xe2x80x83III
in which
R3 and R4, independently of one another, are H or an alkyl radical having 1-12 carbon atoms, in which, in addition, one or more CH2 groups may each, independently of one another, be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 in such a way that heteroatoms are not connected directly, 
A* is
A7, independently of one another if it occurs more than once, is a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
xe2x80x83where this radical may be monosubstituted by Cl or F, 
m is 0, 1, 2 or 3,
r is 0 or 1, and
Z6 and Z7 are as defined above,
where
m+r is 1, 2 or 3,
with the proviso that compounds of the formula I
in which
m is 1,
r is 0,
Z6 is a single bond,
A7 is cyclohexane-1,4-diyl
and
R3 and R4 are an alkyl group, in which, in addition, one CH2 group may be replaced by xe2x80x94Oxe2x80x94,
are excluded.
The compounds of the formula III can be used for the preparation of the compounds of the formula I or preferably can themselves be employed as components of liquid-crystalline media.
The compounds of the formula III can be used to obtain stable liquid-crystalline media, in particular suitable for TFT or STN displays. The novel compounds are distinguished, in particular, by high thermal stability, which is advantageous for a high holding ratio, and exhibit favourable clearing point values. Furthermore, they have particularly low optical anisotropy xcex94n and negative dielectric anisotropy xcex94xcex5.
Liquid-crystalline media having very low optical anisotropy values are of particular importance for reflective and transflective applications, i.e. applications in which the respective LCD experiences no or only supporting background illumination. Low xcex94n values are achieved, in particular, using compounds of the formula I which contain no aromatic rings.
The provision of compounds of the formula III very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
JP 5 279 279 discloses similar difluorocyclohexanes. However, this document only describes compounds having two ring members, which are excluded from formula III by the proviso.
Furthermore, difluorocyclohexanes containing three ring members are described in JP 5 058 926. This document relates exclusively to compounds in which the difluorocyclohexane ring is arranged between two rings, but not to the compounds of formula III of the present invention, which contain a terminal difluorocyclohexane ring.
The compounds of the formula III according to the invention are, in addition, covered by the very broad generic claim of DE 4427266, which is directed towards synthesis intermediates. The difluorocyclohexane derivatives of the present application are, however, not explicitly mentioned therein.
The compounds of the formula III have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add compounds of the formula III to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity. The addition of compounds of the formula III to liquid-crystalline dielectrics allows the xcex94n values of such media to be significantly reduced.
The meaning of the formula III covers all isotopes of the chemical elements bound in the compounds of the formula III. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for producing chiral mesophases.
In the pure state, the compounds of the formula III are colorless and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. They are stable chemically, thermally and to light.
The invention thus furthermore relates to the compounds of the formula III and to the use of these compounds as components of liquid-crystalline media. The invention furthermore relates to liquid-crystalline media comprising at least one compound of the formula III, and to liquid-crystal display elements, in particular electro-optical display elements, which contain media of this type.
Above and below, R1, R2, R3, R4, A*, A4, A5, A6, A7, Z5, Z6, Z7, Z8, Q, r, m, n, p and B* are as defined above, unless expressly stated otherwise. If the radical A7 occurs more than once, it can have the same or different meanings. The same applies to all other groups which occur more than once.
F-substituted cyclohexane-1,4-diyl below is preferably: 
PheFF below is preferably: 
The formula III covers the preferred compounds of the sub-formulae IIIa1 to IIIa6, which, in addition to the group A*, contain one six-membered ring:
R3xe2x80x94A*xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIa1
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIa2
R3xe2x80x94A*xe2x80x94Dioxe2x80x94R4xe2x80x83xe2x80x83IIIa3
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Dioxe2x80x94R4xe2x80x83xe2x80x83IIIa4
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIa5
R3xe2x80x94A*xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIa6
furthermore the likewise preferred compounds of the sub-formulae IIIb1 to IIIb19, which, in addition to the group A*, contain two six-membered rings:
R3xe2x80x94A*xe2x80x94Cycxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb1
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb2
R3xe2x80x94A*xe2x80x94Dioxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb3
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Dioxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb4
R3xe2x80x94A*xe2x80x94CYCxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb5
R3xe2x80x94A*xe2x80x94Dioxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb6
R3xe2x80x94A*xe2x80x94Cycxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb7
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94CYCxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb8
R3xe2x80x94A*xe2x80x94Dioxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb9
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Dioxe2x80x94Dioxe2x80x94R4xe2x80x83xe2x80x83IIIb10
R3xe2x80x94A*xe2x80x94Phrxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb11
R3xe2x80x94A*xe2x80x94Phexe2x80x94CH2CH2xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb12
R3xe2x80x94A*xe2x80x94Dioxe2x80x94CH2CH2xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb13
R3xe2x80x94A*xe2x80x94Cycxe2x80x94COOxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb14
R3xe2x80x94A*xe2x80x94Dioxe2x80x94COOxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb15
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb16
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Dioxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIb17
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94CYCxe2x80x94CH2CH2xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb18
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Dioxe2x80x94CH2CH2xe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIb19
and the preferred compounds of the sub-formulae IIIc1 to IIIc10, which, in addition to the group A*, contain three six-membered rings:
R3xe2x80x94A*xe2x80x94Cycxe2x80x94Cycxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc1
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94Cycxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc2
R3xe2x80x94A*xe2x80x94Cycxe2x80x94Cycxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIc3
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94Phexe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIc4
R3xe2x80x94A*xe2x80x94Cycxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc5
R3xe2x80x94A*xe2x80x94Cycxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94PheFFxe2x80x94R4xe2x80x83xe2x80x83IIIc6
R3xe2x80x94A*xe2x80x94Cycxe2x80x94Dioxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc7
R3xe2x80x94A*xe2x80x94CH2CH2xe2x80x94Cycxe2x80x94Dioxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc8
R3xe2x80x94A*xe2x80x94Cycxe2x80x94CH2CH2xe2x80x94Dioxe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc9
R3xe2x80x94A*xe2x80x94Cycxe2x80x94Dioxe2x80x94CH2CH2xe2x80x94Cycxe2x80x94R4xe2x80x83xe2x80x83IIIc10
in which R3, A*, PheFF, Phe, Cyc, Dio and R4 are as defined above.
R3 and R4 are preferably, independently of one another, straight-chain alkyl or alkoxy having 1 to 10 carbon atoms; alkenyl or alkenyloxy having 2 to 10 carbon atoms; in particular alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl having 2 to 7 carbon atoms.
Preference is furthermore given to compounds of the formula I in which the radicals R3 and R4 or both radicals simultaneously are alkenyl having 2 to 7 carbon atoms.
If the radical R4 is bonded to an aromatic ring, it is preferably alkoxy.
Particular preference is furthermore given to compounds of the formula I in which A7 has one of the following meanings: 
m is preferably 0, 1 or 2, in particular 0 or 1,
m+r is preferably 1 or 2,
Z6 and Z7 are preferably, independently of one another, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or a single bond, particularly preferably a single bond or xe2x80x94CH2xe2x80x94CH2xe2x80x94.
Particular preference is given to the compounds of the formulae IIIA, IIIB, IIIC, IIID and IIIE: 
in which R3, R4 and A* are as defined above, Z6 and Z7 are a single bond or xe2x80x94CH2CH2xe2x80x94, in particular a single bond, and R5 and R6 are as defined for R3 and R4, where at least one of the radicals R5 and R6 is alkenyl.
Compounds of the formula III which contain not more than one dioxane ring likewise represent a preferred embodiment of the invention.
Particular preference is furthermore given to the compounds of the formulae III1 to III11 from the following group: 
in which R3, R4, Z6 and Z7 are as defined above.
If R1, R2, R3 and/or R4 in the formulae above and below are an alkyl radical, this can be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl or heptyl, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl or pentadecyl.
If R1, R2, R3 and/or R4 are an alkyl radical in which one CH2 group has been replaced by xe2x80x94Oxe2x80x94, this can be straight-chain or branched. It is preferably straight-chain and has 1 to 10 carbon atoms. Preferably, the first CH2 group of this alkyl radical is replaced by xe2x80x94Oxe2x80x94, so that the radical R1, R2, R3 and/or R4 becomes alkoxy and is preferably methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy or nonyloxy.
Furthermore, one CH2 group elsewhere can also be replaced by xe2x80x94Oxe2x80x94, so that the radical R1, R2, R3 and/or R4 is preferably straight-chain 2-oxapropyl(=methoxy-methyl), 2-(=ethoxymethyl) or 3-oxabutyl(=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4-or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.
If R1, R2, R3 and/or R4 are an alkenyl radical this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, furthermore oct-1-, -2-, -3-, -4-, -5-, -6- -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.
R1, R2, R3 and/or R4 are particularly preferably an alkenyl radical from the following group: 
If R1, R2, R3 and/or R4 are an alkenyloxy radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. It is particularly preferably a radical from the following group: 
If R1, R2 R3 and/or R4 are an alkyl radical in which one CH2 group has been replaced by xe2x80x94Oxe2x80x94 and one has been replaced by xe2x80x94COxe2x80x94, these are preferably adjacent. These thus contain an acyloxy group xe2x80x94COxe2x80x94Oxe2x80x94 or an oxycarbonyl group xe2x80x94Oxe2x80x94COxe2x80x94. These are preferably straight-chain and have 2 to 6 carbon atoms.
Accordingly, they are in particular acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.
If R1, R2, R3 and/or R4 are an alkyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain. Halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resultant radicals also include perfluorinated radicals. In the case of mono-substitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the xcfx89-position.
Compounds of the formula I containing a branched wing group R1, R2, R3 and/or R4 may occasionally be of importance owing to better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials.
Branched groups of this type generally contain not more than one chain branch. Preferred branched radicals R1, R2, R3 and/or R4 are isopropyl, 2-butyl(=1-methylpropyl), isobutyl(=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentyloxy, 3-methylpentyloxy, 2-ethylhexyloxy, 1-methylhexyloxy or 1-methylheptyloxy.
The formulae I, II and III cover the racemates of these compounds and the optical antipodes, and mixtures thereof.
Of these compounds of the formulae I, II and III and the sub-formulae, preference is given to those in which at least one of the radicals present therein has one of the preferred meanings indicated. Some very particularly preferred smaller groups of compounds of the formula III are those of the sub-formulae III12 to III26: 
in which R3, R4, R5 and R6 are as defined above.
The compounds of the formulae I, II and III are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions.
Use can be made here of variants which are known per se, but are not mentioned here in greater detail.
The starting materials can, if desired, also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the formula I, II or III.
The compounds of the formulae II and III which contain an axially fluorinated 1,4-cyclohexanediyl can be synthesized using hydrogen fluoride under pressure or by means of amine/hydrogen fluoride adducts (for example A. V. Grosse, C. B. Linn, J. Org. Chem. 3, (1938) 26; G. A. Olah, M. Nojima, I. Kerekes, Synthesis (1973) 779; G. A. Olah, X-Y. Li, Q. Wang, G. K. S. Prakash, Synthesis (1993) 693).
It is likewise possible to obtain the compounds of the formula I by simultaneously eliminating HF from a Z5, Z6, Z7 or Z8 bridge and an A* ring by means of a base.
The compounds according to the invention can be prepared, for example, as shown in the following reaction schemes: 
a) 1. R3MgBr, THF; 2. Cat. TsOH, toluene, azeotropic removal of water. b) 1. BH3-THF; 2. H2O2, NaOH; 3. Crystallization from n-heptane. c) PCC, CH2Cl2. d) DAST, CH2Cl2. 
R=alkyl
a) 1. RMgBr, THF; 2. Cat. TsOH, toluene, azeotropic removal of water. b) 1. BH3-THF; 2. H2O2, NaOH; 3. Crystallization from n-heptane. c) PCC, CH2Cl2. d) DAST, CH2Cl2. 
R=alkyl
a) 1. BnOCH2MgBr, THF; 2. Cat. TsOH, toluene, azeotropic removal of water. b) 1. BH3-THF; 2. H2O2, NaOH; 3. Crystallization from n-heptane. C) PCC, CH2Cl2. d) DAST, CH2Cl2. e) H2, 5% Pd/C. f) PCC, CH2Cl2. g) Ph3Pxe2x95x90CHR. 
R=alkyl
a) 1. BnOCH2MgBr, THF; 2. Cat. TsOH, toluene, azeotropic removal of water. b) 1. BH3-THF; 2. H2O2, NaOH; 3. Crystallization from n-heptane. c) PCC, CH2Cl2. d) DAST, CH2Cl2. e) H2, 5% Pd/C. f) PCC, CH2Cl2. g) Ph3Pxe2x95x90CHR. 
in which R1, R2, R3 and R4 are as defined above.
Esters of the formula I can also be obtained by esterification of corresponding carboxylic acids (or reactive derivatives thereof) using alcohols or phenols (or reactive derivatives thereof) or by the DCC method (DCC=dicyclohexylcarbodiimide).
The corresponding carboxylic acids and alcohols or phenols are known or can be prepared analogously to known processes.
Suitable reactive derivatives of said carboxylic acids are in particular the acid halides, especially the chlorides and bromides, furthermore the anhydrides, azides or esters, in particular alkyl esters having 1-4 carbon atoms in the alkyl group.
Suitable reactive derivatives of said alcohols are in particular the corresponding metal alkoxides, preferably of an alkali metal, such as Na or K.
The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable solvents are ethers, such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones, such as acetone, butanone or cyclohexanone, amides, such as DMF or hexamethylphosphoric triamide, hydrocarbons, such as benzene, toluene or xylene, halogenated hydrocarbons, such as tetrachloromethane or tetrachloroethylene, and sulphoxides, such as dimethyl sulphoxide or sulpholane. Water-immiscible solvents can at the same time advantageously be used for removal by azeotropic distillation of the water formed during the esterification. It may in some cases also be possible to use an excess of an organic base, for example pyridine, quinoline or triethylamine, as solvent for the esterification. The esterification can also be carried out in the absence of a solvent, for example by simply heating the components in the presence of sodium acetate. The reaction temperature is usually between xe2x88x9250xc2x0 and +250xc2x0, preferably between xe2x88x9220xc2x0 and +80xc2x0. At these temperatures, the esterification reactions are generally complete after from 15 minutes to 48 hours.
In detail, the reaction conditions for the esterification depend substantially on the nature of the starting materials used. Thus, the reaction of a free carboxylic acid with a free alcohol is generally carried out in the presence of a strong acid, for example a mineral acid, such as hydrochloric acid or sulphuric acid. A preferred reaction procedure is to react an acid anhydride or, in particular, an acid chloride with an alcohol, preferably in a basic medium, important bases being, in particular, alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal carbonates or hydrogencarbonates, such as sodium carbonate, sodium hydrogencarbonate, potassium carbonate or potassium hydrogencarbonate, alkali metal acetates, such as sodium acetate or potassium acetate, alkaline-earth metal hydroxides, such as calcium hydroxide, or organic bases, such as triethylamine, pyridine, lutidine, collidine or quinoline. A further preferred embodiment of the esterification comprises first converting the alcohol into the sodium or potassium alkoxide, for example by treatment with ethanolic sodium hydroxide or potassium hydroxide solution, and isolating the product and reacting it with an acid anhydride or, in particular, acid chloride.
Nitriles can be obtained by replacement of halogens using copper cyanide or alkali metal cyanide.
Ethers of the formulae I, II and III are obtainable by etherification of corresponding hydroxyl compounds, the hydroxyl compound advantageously first being converted into a corresponding metal derivative, for example into the corresponding alkali metal alkoxide, by treatment with NaH, NaNH2, NaOH, KOH, Na2CO3 or K2CO3. This metal derivative can then be reacted with the appropriate alkyl halide, alkyl sulphonate or dialkyl sulphate, advantageously in an inert solvent, such as, for example, acetone, 1,2-dimethoxyethane, DMF or dimethyl sulphoxide, or alternatively with an excess of aqueous or aqueous-alcoholic NaOH or KOH, at temperatures between about 20xc2x0 C. and 100xc2x0 C.
The organometallic compounds are prepared, for example, by metal-halogen exchange (for example in accordance with Org. React. 6, 339-366 (1951)) between the corresponding halogen compound and an organolithium compound, such as, preferably, tert-butyllithium or lithium naphthalenide, or by reaction with magnesium turnings.
In addition, the compounds of the formulae I, II and III can be prepared by reducing a compound which contains one or more reducible groups and/or Cxe2x80x94C bonds in place of H atoms, but otherwise conforms to the formulae I, II and III.
Suitable reducible groups are preferably carbonyl groups, in particular keto groups, furthermore, for example, free or esterified hydroxyl groups or aromatically bonded halogen atoms. Preferred starting materials for the reduction are compounds which conform to the formulae I, II and III, but contain a cyclohexene ring or cyclohexanone ring in place of a cyclohexane ring and/or contain a xe2x80x94CHxe2x95x90CHxe2x80x94 group in place of a xe2x80x94CH2CH2xe2x80x94 group and/or contain a xe2x80x94COxe2x80x94 group in place of a xe2x80x94CH2xe2x80x94 group and/or contain a free or functionally derived (for example in the form of its p-toluenesulphonate) OH group in place of an H atom.
The reduction can be carried out, for example, by catalytic hydrogenation at temperatures between about 0xc2x0 and about 200xc2x0 C. and at pressures between about 1 and 200 bar in an inert solvent, for example an alcohol, such as methanol, ethanol or isopropanol, an ether, such as tetrahydrofuran (THF) or dioxane, an ester, such as ethyl acetate, a carboxylic acid, such as acetic acid, or a hydrocarbon, such as cyclohexane. Suitable catalysts are advantageously noble metals, such as Pt or Pd, which may be employed in the form of oxides (for example PtO2 or PdO), on a support (for example Pd on carbon, calcium carbonate or strontium carbonate) or in finely divided form.
Ketones can also be reduced by the methods of Clemmensen (using zinc, zinc amalgam or tin and hydrochloric acid, advantageously in aqueous-alcoholic solution or in the heterogeneous phase with water/toluene at temperatures between about 80 and 120xc2x0 C.) or Wolff-Kishner (using hydrazine, advantageously in the presence of alkali, such as KOH or NaOH, in a high-boiling solvent, such as diethylene glycol or triethylene glycol, at temperatures between about 100 and 200xc2x0 C.) to give the corresponding compounds of the formulae I, II and III which contain alkyl groups and/or xe2x80x94CH2CH2xe2x80x94 bridges.
Furthermore, reductions using complex hydrides are possible. For example, arylsulphonyloxy groups can be removed reductively using LiAlH4, in particular p-toluenesulphonyloxymethyl groups can be reduced to methyl groups, advantageously in an inert solvent, such as diethyl ether or THF, at temperatures between about 0 and 100xc2x0 C.
Double bonds can be hydrogenated using NaBH4 or tributyltin hydride in methanol.
The starting materials are either known or can be prepared analogously to known compounds.
The liquid-crystalline media according to the invention preferably comprise from 2 to 40 components, in particular from 4 to 30 components, as further constituents besides one or more compounds according to the invention. These media very particularly preferably comprise from 7 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenyl or cyclohexyl cyclohexylbenzoates, phenyl or cyclohexyl cyclohexylcyclohexanecarboxylates, cyclohexylphenyl benzoates, cyclohexanecarboxylates and cyclohexylcyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4xe2x80x2-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylyl-ethanes, 1-phenyl-2-cyclohexylphenylethanes optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most important compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5:
Rxe2x80x2xe2x80x94Lxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x831
Rxe2x80x2xe2x80x94Lxe2x80x94COOxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x832
Rxe2x80x2xe2x80x94Lxe2x80x94OOCxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x833
Rxe2x80x2xe2x80x94Lxe2x80x94CH2CH2xe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x834
Rxe2x80x2xe2x80x94Lxe2x80x94Cxe2x89xa1Cxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x835
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are in each case, independently of one another, a bivalent radical from the group formed by xe2x80x94Phexe2x80x94, xe2x80x94Cycxe2x80x94, xe2x80x94Phrxe2x80x94Phexe2x80x94, xe2x80x94Phexe2x80x94Cycxe2x80x94, xe2x80x94Cycxe2x80x94Cycxe2x80x94, xe2x80x94Pyrxe2x80x94, xe2x80x94Dioxe2x80x94, xe2x80x94Gxe2x80x94Phexe2x80x94 and xe2x80x94Gxe2x80x94Cycxe2x80x94 and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phexe2x80x94Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of xe2x80x94Phrxe2x80x94Phexe2x80x94, xe2x80x94Phexe2x80x94Cycxe2x80x94, xe2x80x94Cycxe2x80x94Cycxe2x80x94, xe2x80x94Gxe2x80x94Phexe2x80x94 and xe2x80x94Gxe2x80x94Cycxe2x80x94, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of xe2x80x94Phexe2x80x94Cycxe2x80x94, xe2x80x94Cycxe2x80x94Cycxe2x80x94, xe2x80x94Gxe2x80x94Phe-xe2x80x94 and xe2x80x94Gxe2x80x94Cycxe2x80x94.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are denoted by the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, which is called group B, Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3xe2x88x92(k+1)FkCl1, where i is 0 or 1, and k and 1 are 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are denoted by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is xe2x80x94CN; this sub-group is called group C below, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.
In addition to the preferred compounds of groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents are also customary. All these substances can be obtained by methods which are known from the literature or analogously thereto.
Besides compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from Group A and/or Group B and/or Group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably:
Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90%
Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65%
Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50%, the sum of the proportions by weight of the group A and/or B and/or C compounds present in the particular media according to the invention preferably being 5%-90% and in particular from 10% to 90%.
The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 5 to 30%, of the compounds according to the invention. Preference is furthermore given to media which comprise more than 40%, in particular from 45 to 90%, of compounds according to the invention. The media preferably comprise three, four or five compounds according to the invention.
The media according to the invention are prepared in a manner which is customary per se. In general, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases can be modified in accordance with the invention in such a manner that they can be used in all types of liquid-crystal display elements which have been disclosed hitherto. Additives of this type are known to those skilled in the art and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added for the production of coloured guest-host systems, or substances can be added to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding German Application 19914683.7, filed Mar. 31, 1999, Germany Patent Application No. 19914684.5, filed Mar. 31, 1999, and German Patent Application No. 19919435.1, filed Apr. 29, 1999, is hereby incorporated by reference.